Sundays River Research Articles

Digital twins to quantify the impact of growing variability on the harvest quality of orange

The quality of citrus fruit is influenced by various growing conditions, including weather. However, the impact of weather differences between growing regions on citrus quality at harvest is not well understood. This study employs a mechanistic-driven digital replica of the growth process of a Valencia orange from fruit set until harvest to quantify this impact. Measured daily temperature, humidity, rainfall, solar radiation, and wind speed data from various orange growing regions of South Africa, including Citrusdal, Nelspruit, Letsitele, and Sundays River Valley (SRV), inform and drive this digital model. The results suggest that the differences in weather conditions between growing regions significantly affect fruit diameter (FD), fruit weight (FW), rind thickness (RT), rind weight (RW), total soluble solids (TSS), titratable acidity (TA), and °Brix/acid ratio of oranges at harvest. The differences between growing regions led to variations of up to threefold for FD, twofold for FW, RT, RW, TSS, °Brix/acid ratio and up to fourfold for TA upon harvest. Particularly, oranges produced from warmer Letsitele and Nelspruit regions are found to be larger, sweeter and less acidic compared to those from coastal SRV upon harvest. The study also reveals the impact of the fruit growth process on the temperature gradient within the fruit, which varies across growing regions. The maximal temperature difference between the fruit core and surface during the growth process ranges from 4 °C to ∼7 °C. These variations in fruit temperature gradient could lead to variations in temperature-driven quality decay of fruit from different climatic regions at the start of their postharvest journey. These findings provide valuable insights for the citrus industry, aiding to optimize practices, harvest planning, and postharvest logistics. The output of this digital twin will help identify areas needing extra precooling to extend postharvest shelf life and minimize quality decay. Real-world use allows growers to schedule harvests based on regional weather conditions.

Utilization of hydrodynamic modelling to quantify water losses from the Sundays River between Darlington Dam and Korhaans Drift Weir

This study quantified transfer losses over the 2021/2022 water year for irrigation releases from Darlington Dam into the Sundays River, which are diverted at the Korhaans Drift Weir. A one-dimensional (1D) hydrodynamic model was set up and calibrated to simulate the transfer losses which were assumed to consist primarily of evaporation and evapotranspiration (ET). Flow measurements were undertaken with an acoustic doppler current profiler (ADCP) to verify the calibrations of the Parshall flumes at Darlington Dam and at Korhaans Drift Weir. The ADCP results showed that the Department of Water and Sanitation’s (DWS’s) existing discharge tables underestimated lower flows by 13% and higher flows by 16%. The hydrodynamic model results also estimated transfer losses between Darlington Dam and Korhaans Drift to range between 2.0% and 5.3%. It was determined that the transfer losses were seasonal and were lower than those determined by similar studies for other South African rivers.

Occurrence of virulence determinants in vibrio cholerae, vibrio mimicus, vibrio alginolyticus, and vibrio parahaemolyticus isolates from important water resources of Eastern Cape, South Africa

BackgroundVirulence determinants are crucial to the risk assessment of pathogens in an environment. This study investigated the presence of eleven key virulence-associated genes in Vibrio cholerae (n = 111) and Vibrio mimicus (n = 22) and eight virulence determinants in Vibrio alginolyticus (n = 65) and Vibrio parahaemolyticus (n = 17) isolated from six important water resources in Eastern Cape, South Africa, using PCR techniques. The multiple virulence gene indexes (MVGI) for sampling sites and isolates as well as hotspots for potential vibriosis outbreaks among sampling sites were determined statistically based on the comparison of MVGI.ResultThe PCR assay showed that all the V. cholerae isolates belong to non-O1/non-O139 serogroups. Of the isolates, Vibrio Cholera (84%), V. mimicus (73%), V. alginolyticus (91%) and V. parahaemolyticus (100%) isolates harboured at least one of the virulence-associated genes investigated. The virulence gene combinations detected in isolates varied at sampling site and across sites. Typical virulence-associated determinants of V. cholerae were detected in V. mimicus while that of V. parahaemolyticus were detected in V. alginolyticus. The isolates with the highest MVGI were recovered from three estuaries (Sunday river, Swartkopps river, buffalo river) and a freshwater resource (Lashinton river). The cumulative MVGI for V. cholerae, V. mimicus, V. alginolyticus and V. parahaemolyticus isolates were 0.34, 0.20, 0.45, and 0.40 respectively. The targeted Vibrio spp. in increasing order of the public health risk posed in our study areas based on the MVGI is V. alginolyticus > V. parahaemolyticus > V. cholerae > V. mimicus. Five (sites SR, PA5, PA6, EL4 and EL6) out of the seventeen sampling sites were detected as the hotspots for potential cholera-like infection and vibriosis outbreaks.ConclusionsOur findings suggest that humans having contact with water resources in our study areas are exposed to potential public health risks owing to the detection of virulent determinants in human pathogenic Vibrio spp. recovered from the water resources. The study affirms the relevancy of environmental Vibrio species to the epidemiology of vibriosis, cholera and cholera-like infections. Hence we suggest a monitoring program for human pathogenic Vibrio spp. in the environment most especially surface water that humans have contact with regularly.

Cosmogenic nuclide burial dating at Penhill Farm: An Earlier Stone Age Acheulean locality in the lower Sundays River Valley, South Africa

Cosmogenic nuclide burial dating at Penhill Farm: An Earlier Stone Age Acheulean locality in the lower Sundays River Valley, South Africa

Trophic ecology of co-occurring fishes in the Sundays River Valley irrigation ponds, assessed using stable isotope and gut content analyses.

The analysis of food web structures has increased the understanding of the dynamics of organisms belonging to different trophic levels. In this study, the diet of two native species, Glossogobius callidus and Gilchristella aestuaria, was assessed in the presence of two non-native species, Oreochromis mossambicus and Gambusia affinis, in irrigation ponds, Eastern Cape Province, South Africa. The proportion of dietary items consumed and assimilated by the four fish species were inferred from gut contents and carbon and nitrogen stable isotope analysis. Stable isotope analysis revealed that both G. affinis and O. mossambicus had a larger isotopic niche size than G. callidus and G. aestuaria. Although G. callidus fed on benthic resources and G. aestuaria fed on phytoplankton, gut content analysis showed that G. callidus, O. mossambicus and G. affinis fed predominantly on benthic resources, whereas G. aestuaria fed mainly on plankton resources. Considerable niche overlap corroborates the view that resource competition is a major factor shaping the composition of the four fish species. This study highlighted the low diversity of the food web within the Sundays River Valley irrigation ponds, where food items are shared by all the small-bodied fishes.

Brevipalpus (Tenuipalpidae) and orchid fleck virus (OFV) in South Africa: what do we know?

Certain species of Brevipalpus (Trombidiformes: Tenuipalpidae) are able to transmit viruses of the citrus leprosis complex, a serious non-systemic disease of citrus. This disease is endemic to Central and South America, and is characterised by necrotic lesions with chlorotic halos on twigs, leaves and fruit. Citrus leprosis is caused by two types of RNA viruses: cytoplasmic (CL-C) and nuclear (CL-N). In South Africa, CL-N symptoms were detected in 2018 in citrus orchards in the Sundays River Valley (SRV) of the Eastern Cape (Fig 1), and found to be associated with trees testing positive for orchid fleck virus (OFV) (Cook et al. 2019). Mites from this site identified as B. californicus s.l. tested positive for OFV. It is assumed that the entry pathway of OFV virus into South Africa was via the trade of orchid pot plants, and that it was then transmitted to citrus by viruliferous B. californicus. This is the first CL virus-vector association and putative transmission from orchids to citrus identified in South Africa.

Seasonal variation and drivers of zooplankton, macroinvertebrate and littoral fish communities from irrigation ponds in a semi-arid region in the Eastern Cape (South Africa)

Irrigation ponds are increasingly abundant globally, particularly in water-stressed countries with limited natural surface waters, yet knowledge of their ecology is limited. Here, we assessed zooplankton, macroinvertebrate, and littoral fish communities from irrigation ponds located in the Sundays River Valley in South Africa. This study assessed the seasonal community patterns in response to physico-chemical and biotic components. Water temperature, water depth, Secchi depth, and ammonium concentrations differed significantly across seasons. Similarly, Chlorophyll-a concentrations differed seasonally, with water transparency identified as the main driver. Zooplankton was dominated by Rotifera, Copepoda and Cladocera. Seasonal changes in temperature and subsequent fluctuations in water levels resulted in changes in zooplankton community. Macroinvertebrates were dominated by insects, notably the families Corixidae and Naucoridae. The littoral fish community comprised of Glossogobius callidus, Oreochromis mossambicus and Gambusia affinis. Zooplankton, macroinvertebrates and littoral fish abundances, species richness, diversity and assemblage composition differed significantly across seasons with temperature identified as the main driver of these differences. This study demonstrates that bottom-up processes are the dominant drivers of the irrigation pond communities in the Sundays River Valley and highlights the relevance of seasonal abiotic drivers in structuring these communities, particularly G. callidus and G. affinis.

Occurrence and distribution of pharmaceuticals in surface water and sediment of Buffalo and Sundays River estuaries, South Africa and their ecological risk assessment

This study investigated the presence of pharmaceuticals in the water and sediment of Buffalo and Sundays River Estuary, South Africa. Extraction for water and sediment samples was achieved with solid-phase extraction and ultrasonic extraction methods, respectively. Quantification of the target analytes was done with UPLC-QTOF-MS. The pH of surface water in all the sampling sites (8.18–10.1) were above the WHO guideline (6.5). A good correlation was observed between the concentrations of analytes with organic matter and organic carbon. Results showed that carbamazepine exhibited the highest concentration (8.75 ± 1.45 μg/kg) of all the pharmaceuticals, while trimethoprim has the highest detection frequency with the highest concentration of 1.62 ± 0.83 μg/kg in the sediment samples. Sulfamethoxazole was below the detection limit in both estuaries. Calculated risk quotients revealed that carbamazepine and trimethoprim could be of potential risk, while caffeine may pose a very low risk to the aquatic organisms investigated. Proper monitoring of the runoff entering Buffalo Estuary is required, being the point of discharge of Buffalo River to the Indian Ocean. Also, the domestic waste discharge from residences in the surroundings of Sundays Estuary should be monitored.

Filling in the knowledge gap: Observing MacroPlastic litter in South Africa's rivers

Only 12% of the world's published plastic research includes references to Africa despite it being a significant contributor to the global plastic waste and mismanagement problem (~88.5% of Africa's plastic waste is mismanaged). Ocean plastics are transported from land by rivers to the sea. However, source contextualization is complex. Many African rivers predominantly run alongside human settlements that host informal waste dumpsites. In this study a simple cost effective, easily deployed, consistent and replicable survey methodology was employed. The study quantified macroplastic in three rivers discharging into Algoa Bay, South Africa. The results indicated that industrial Swartkops and metropolitan Baakens Rivers both illustrate moderate plastic pollution (>3000 plastic particles/day), with the relatively natural Sundays River to showing minimal evidence of river macro plastic (<100 plastic particles/day). The types of plastic were noted using the RIMMEL app (premier African implementation), enabling proportional comparison of different plastic litter types to be completed.

Life history of the river goby Glossogobius callidus (Teleostei: Gobiidae).

The river goby Glossogobius callidus is native to freshwater and estuarine habitats in South Africa. Individuals [21.1-144.4 mm total length (LT )] were sampled from impoundments in the Sundays River Valley, Eastern Cape, from February 2014 to March 2015. The largest female was 137.2 mm LT , and the largest male was 144.4 mm LT . Length-at-50% maturity was 75.2 ± 2.1 mm LT for males and 76.2 ± 2.0 mm LT for females. Absolute fecundity was 1028.2 ± 131.7 oocytes per fish, and relative fecundity was 50.1 ± 18.1 oocytes per gram. The spawning season extended from October to December. Fish were aged using sectioned sagittal otoliths. The growth zone periodicity was validated using edge analysis. Longevity was more than 7 years for females and more than 6 years for males. Length-at-age was similar for the two sexes and was best described using the von Bertalanffy growth model as Lt = 74.7(1 - e-1.0(t + 0.1) ) mm LT for the entire population. Using the population age structure, the mortality rate was estimated at 1.3 per year.

The suitability of a low temperature post-IR IRSL signal for dating alluvial and colluvial “cut and fill” sequences in the Great Karoo, South Africa

Abstract Alluvial and colluvial “cut and fill” deposits preserved in valleys of the Karoo, South Africa, reflect basin-scale adjustments in fluvial process-regime. Such deposits in the Wilgerbosch catchment have previously proven difficult to date using radiocarbon (14C) and optically stimulated luminescence (OSL) methods. In this paper, we test the suitability of K-feldspar post-IR infrared (pIRIR) methods on 19 samples from Africanders Kloof, a low-order tributary of the Sundays River. Using three carefully screened quartz OSL ages, radiocarbon dating and site stratigraphic considerations we argue that the pIRIR170 protocol can be used to produce reliable age estimates. Fading rates for the pIRIR170 signal are consistently low (average g2days: 0.81 ± 0.58). The pIRIR170 residuals are dose dependent (r2 = 0.58); but are consistently low as a proportion (e.g. 1–4%) of sample equivalent dose (De). Despite the water-lain depositional context, single aliquot De distributions tend toward normality (for 11/19 samples) irrespective of aliquot size (2 mm or micro-aliquots containing 2–30 grains) with only a few statistical outliers per sample (max. n = 3) and overdispersion (OD) ranging from 1.6 to 30% excluding the two youngest (late Holocene) samples (OD: 37–87%). The resulting pIRIR170 ages are in the correct stratigraphic order and illustrate the potential of pIRIR170 luminescence dating to investigate the timing, processes and drivers of fluvial system adjustments across the Karoo.

Gordon research conference 2019: From the biophysics of natural and artificial photosynthesis to bioenergy conversion

Here, we provide a brief report on the 2019 Gordon Research Conference (GRC) and Gordon Research Seminar (GRS) on photosynthesis. Both the GRC (July 21–26, 2019) and GRS (July 20–21, 2019) were held at Sunday River Resort, Maine, USA, bringing together the beginners as well as the established scientists to discuss recent advances in photosynthesis research.

Diet of Glossogobius callidus (Teleostei: Gobiidae) in freshwater impoundments in the Sundays River Valley of the Eastern Cape, South Africa

Despite the high abundance of the gobiid fish Glossogobius callidus in many freshwater ecosystems in South Africa, very few studies have assessed the biology and ecology of the species. Here, we investigated the diet of G. callidus populations sourced from Sundays River irrigation ponds. A total of 571 fish grouped into two size classes (TL, range ± SD: juveniles of 20–60 ± 45 mm; adults of 61–140 ± 85 mm) were sampled by seine netting; prey items were removed from the guts and identified and sorted to obtain dietary information for each prey group. Of the examined guts, 97% contained prey comprising 17 taxa within 10 taxonomic groups. Teleosts were identified to species level, whereas most dietary components were identified to a broad taxonomic group. Aquatic invertebrates were the most important component of the diet of G. callidus, but the index of relative importance (%IRI) of dominant invertebrate taxa varied according to ontogenetic stage of G. callidus and season. Prey taxa included: Diptera, Hemiptera, Trichoptera, Odonata, Cladocera, Copepoda, Hydracarina, Amphipoda, Mollusca and Teleostei. Dipteran prey taxa were consistently encountered in both size classes and across all seasons. G. callidus can therefore be regarded as a generalist invertivore.

Molecular and morphological evidence reveals hybridisation between two endemic cyprinid fishes.

The geographic occurrence of moggel Labeo umbratus × mud fish Labeo capensis hybrids and the threat of hybridisation to the genetic integrity of L. umbratus were investigated. Genetic evidence from mtDNA cytb and nDNA s7 intron sequence data indicated probable interspecific hybridisation in two impoundments, Hardap Dam (Orange River Basin, Namibia) and Darlington Dam (Sundays River Basin, Eastern Cape, South Africa). Some putative hybrids were morphologically identifiable on account of their meristic and morphometric intermediacy to the parent species. Human activities appear to drive the observed hybridisation, either through dam construction and direct stocking of L. umbratus or via translocation of Labeo capensis and the previously isolated Orange River lineage of L. umbratus into the southern-flowing systems by inter-basin water transfers. It is recommended that further translocation of fish from these areas should be avoided.

Distribution of organochlorine pesticides in fresh fish carcasses from selected estuaries in Eastern Cape Province, South Africa, and the associated health risk assessment

Abstract In this study, gills and muscles tissue samples from 30 specimens of P. commersonnii and 22 specimens of M. cephalus obtained from Swartkops and Sundays River Estuaries respectively were analysed for OCPs using GC-μECD, and their risk assessments were performed using the standard protocol described by the US EPA. These species were targeted due to their relative abundance in their respective estuaries. Our findings indicate that from all the fish samples analysed only two samples of P. commersonnii did not contain the target analytes. The risk assessment showed that the hazard ratios (HRs) for cancer risk for all OCPs in muscles of both fish species were less than unity. Thus, this indicates that the daily exposure to the targeted OCPs based on the consumption of these fish species do not have a lifetime cancer risk. The HR values for non-cancer risk were all less than 1.

Development of the Sterile Insect Technique to Suppress Thaumatotibia leucotreta (Lepidoptera: Tortricidae) in Citrus Fruit: Commercialisation and Expansion (Part 2)

Progress since 2007 with the commercial implementation of the sterile insect technique (SIT) for Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) in citrus orchards in South Africa is discussed. To enable expansion of the SIT programme, rearing equipment was developed and adapted where necessary. Production monitoring systems for traceability, cold chain management and quality management of reared insects were developed and constantly improved. The initial 3300-ha SIT-treated area in the Citrusdal region was increased to 4800 ha by incorporating parts of the Olifants River Valley and sterile insect releases were also introduced into 6500 and 2200 ha of the Sundays River and Gamtoos River Valleys (Eastern Cape Province), respectively. There was a progressive, seasonal improvement in wild T. leucotreta suppression following routine releases of sterile moths in all areas treated, resulting in reduced crop losses and fewer rejections for T. leucotreta in export fruit. The SIT for T. leucotreta was also expanded to the Hex River Valley (Western Cape Province) and the Lower Orange River area (Northern Cape Province) in 2016.

Occurrence and risk evaluation of organochlorine contaminants in surface water along the course of Swartkops and Sundays River Estuaries, Eastern Cape Province, South Africa.

Organochlorine contaminants were analysed in surface water from Sundays (SDE) and Swartkops Estuaries (SWE), Eastern Cape Province, which is among the largest estuaries in South Africa. The concentration of Σ18OCPs ranged from 16.7 to 249.2ng/L in autumn, 19.9-81.4ng/L in winter, 43.6-126.8ng/L in spring and 68.3-199.9ng/L in summer for SDE, whereas in SWE, the values varied from 20.9 to 259.7ng/L in autumn, 58.9-263.9ng/L in winter, 3.2-183.6ng/L in spring and 118.0-188.9ng/L in summer. Among all OCPs, α-HCH, β-HCH, p,p'-DDE, p,p'-DDT, endrin, dieldrin and endrin aldehyde were predominant in surface water samples from SDE and SWE. Furthermore, the mean concentration of polychlorinated biphenyls (PCBs) ranged from 126.7ng/L in winter to 151.0ng/L in spring for SDE and 249.0ng/L in spring to 727.6ng/L in winter for SWE. Tri- and tetra-PCBs dominated the PCB homologue profile. Hierarchical cluster analysis grouped the study sites into three regions from least polluted to most polluted, indicated that SWE is more polluted compared to SDE, probably due to the influx of agricultural and industrial effluents. Carcinogenic and non-carcinogenic risk assessment revealed that the water from both estuaries is not safe for drinking, although suitable for bathing.

Integrating chemical control with sterile insect releases in an integrated pest management programme for Thaumatotibia leucotreta

AbstractFalse codling moth Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) is an important indigenous pest of citrus in southern Africa. Successful control is dependent upon integration of area‐wide sterile insect releases and other suppression methods. The aim of this work was to test pyrethroid and organophosphate‐based insecticides (tau‐fluvalinate and chlorpyrifos) for their residual effect on mortality of released irradiated T. leucotreta male moths. Both of these insecticides were effective in killing irradiated T. leucotreta for 7 days after application on leaves, after which degradation of the active ingredient resulted in a marked reduction in efficacy after 14 days and rendering them harmless. Mortality was found to be similar for irradiated and non‐irradiated male T. leucotreta after treatment. Consequently, even though these insecticides might have an effect on moths in the field, ratios of sterile:wild moths should not be altered. Supporting field data from six sites in the Sundays River Valley over a season of sterile insect releases showed the conventional chemical crop protection programme to be as effective as an integrated pest management programme in facilitating effective control of T. leucotreta through sterile insect releases. The study also confirmed that the ratios of sterile:wild male moths in the commercial citrus orchards were not affected by the application of insecticides. These findings confirm the high potential of sterile insect releases for control of T. leucotreta in citrus.

Gordon Research Conference on photosynthesis: photosynthetic plasticity from the environment to synthetic systems.

Here, we provide a summary of the 2017 Gordon Research Conference on Photosynthesis: "Photosynthetic plasticity: from the environment to synthetic systems". This conference was held at the Grand Summit Resort Hotel at Sunday River, Newry, Maine, USA, from July 16 to 21, 2017. We have also included here a brief description of the Gordon Research Seminar (for students and post-docs) held during 2days preceding this conference. Following the conclusion of the conference's scientific program, four young scientists (Han Bao, Vivek Tiwari, Setsuko Wakao, and Usha Lingappa) were recognized for their research presentations, each of whom received a book as a gift from one of us (Govindjee). Having chaired the 2015 Gordon Research Conference on Photosynthesis in 2015, Fabrice Rappaport, who lost his fight against cancer in January 2016, was remembered for his profound impact on the field of photosynthesis research.

Valuing user preferences for improvements in public nature trails around the Sundays River Estuary, Eastern Cape, South Africa

Many valuations have been made of changes to in-estuary attributes, but few have been made of out-of-estuary attributes. From a recreation perspective, an important type of out-of-estuary attribute is the availability of public paths by which to access attractive features of the estuary environment. This paper values an improvement in the level of public access in the form of an additional nature trail along the banks of the Sundays River Estuary in the Eastern Cape, but does not compare this value with the costs. By means of choice experiment modelling analyses it is estimated that in 2010 the marginal willingness to pay for an investment in a nature trail was R34 per user per annum. In order to determine whether the development of this trail is efficient, this benefit (R34 per user per annum) needs to be compared to the cost of the development, an analysis that remains to be done. However, this finding does serve to provide guidance on how much funding could efficiently be allocated to such a development – about ZAR1.22 million, assuming a social discount rate of 8.38%.